708 



SPERM, OVA, AND PREGNANCY 



mark now two decades old. In his review 

 many problems were noted, some since 

 solved, others still in the course of solution, 

 and many even yet ignored. 



The major advances in sperm biology 

 during the intervening years have been 

 world-wide and substantial. Stimulated in 

 large measure by the exigencies of the ani- 

 mal-breeding industry. Lardy and co-work- 

 ers at Wisconsin developed biochemical 

 methods and concepts pertaining to sperma- 

 tozoa, particularly those of the bull. Mann 

 and his many able Cambridge colleagues 

 have elucidated major aspects of the meta- 

 bolic and enzymatic activities of sperma- 

 tozoa in several domestic species. Signifi- 

 cant contributions have appeared from 

 various laboratories, too numerous to desig- 

 nate, from the basic demonstrations, by the 

 Engelhardt school, of the role of adenosine 

 triphosphate (ATP) and adenosinetriphos- 

 phatase (ATPase) in the motility of sperm, 

 to the apparently unique metabolic charac- 

 teristics of human spermatozoa reported 

 principally by MacLeod. 



A second major stride in the study of the 

 male gamete has been provided by the de- 

 velopment of the electron microscope. By 

 virtue of the increase in magnification, up 

 to 1000-fold, cells can be visually dissected 

 down to elements on the order of 10 A in 

 size. Not the least of its accomplishments, 

 the electron microscope has made possible 

 the demonstration that all sperm flagella 

 and all cilia throughout the plant and ani- 

 mal kingdoms possess the same basic pat- 

 tern of longitudinal filaments, the well 

 known 2x9 + 2 array. The full signifi- 

 cance of this structural constancy is yet to 

 be realized, but inasmuch as these filaments 

 are generally assumed to represent the mo- 

 tile organelles of the cell, the physicochemi- 

 cal basis for motility may eventually be 

 resolved. Likewise, the electron microscope 

 has facilitated the study of spermatozoa 

 during their maturation and in the initial 

 stages of fertilization. Significant altera- 

 tions in the acrosome, for example, seem to 

 be related to the processes involved in the 

 union of gametes. 



The sperm has, in fact, been more closely 

 scrutinized and is now recognized as some- 

 thing more than a uniform, finished product 



of the spermatogenic process. Mammalian 

 spermatozoa from the same gonad may well 

 differ with respect to phenotypic and anti- 

 genic characteristics. They are, moreover, 

 far from functionally mature as they leave 

 the testis; structural and biochemical 

 changes occur during their sojourn and 

 transport through both the male and female 

 genital tracts such that their capacity for 

 fertilization is enhanced with time and mi- 

 gration. Investigation of these processes 

 constitutes a very active area of research in 

 current studies of reproductive physiology. 



Another important advance in recent 

 years, which may here be singled out for 

 comment, concerns the mechanism of trans- 

 port of spermatozoa through the female gen- 

 ital tract. One of the earliest features of 

 mammalian reproduction to be studied, only 

 recently has the full weight of experimental 

 attack demonstrated the important endo- 

 crinologic role involved in the process. 



These, among other, developments in 

 sperm biology are considered in some detail 

 in the pages that follow. No attempt is made 

 to survey completely the available litera- 

 ture, which is enormous; rather, what seem 

 to be significant current principles and proc- 

 esses are discussed within the scope and 

 space allotments of the present volume. The 

 general characteristics of whole semen and 

 its jiroduction, reviewed elsewhere (see 

 Mann, 1954; chapters by Albert and by 

 Price and Williams-Ashman) , are necessar- 

 ily slighted in favor of a fuller discussion of 

 the internal environment of the male and 

 female genital tracts and the probable con- 

 ditions surrounding the sperm in vivo. For- 

 tunately, a number of recent reviews cover 

 many of the principal, broad points noted 

 above and serve as background for the ma- 

 terial reported here (MacLeod, 1943b; 

 Ivanov, 1945; Mann, 1949, 1954; Austin 

 and Bishop, 1957; Colwin and Colwin, 1957; 

 Fawcett, 1958; Mann and Lutwak-Mann, 

 1958; Bishop, 1961; Tyler and Bishop. 

 1961). 



The function of the male gamete is to 

 serve as activator of the ovum and contribu- 

 tor of paternal hereditary components to the 

 zygote. The sperm thus stimulates an other- 

 wise relatively inert egg and initiates a new 

 course of development. In Weissmannian 



